When I spent a few days with the M23 rebels of eastern Congo in August, they were clear that their April mutiny against the Congolese army and seizure of territory along the Rwandan and Ugandan borders was essentially a form of blackmail. The government of the Democratic Republic of Congo (DRC) and its President Joseph Kabila were weak and corrupt, they said, and constantly tried to cheat, steal from or even kill men from the east — who, like most of the M23, were former rebels integrated into the national army after a similar rebellion in the east in 2009. The mutineers were hardly angels themselves, with a string of human-rights violations to their names, including the recruitment of children, use of rape and sometimes execution of civilians. But they maintained they didn’t necessarily want to take the strategic eastern cities of Goma or Bukavu and certainly didn’t want to advance on the capital, Kinshasa; rather they wanted the government to honor the integration deal it agreed to on March 23, 2009, and since it hadn’t — withholding salaries, integrating soldiers at lower ranks, even continuing to kill a few easterners — the rebels were trying to force it to by taking territory.

I asked: What if Kinshasa still refused to come up with the goods? They’d take Goma, a base for one of the world’s largest U.N. peacekeeping and aid operations, to up their bargaining position and press their point. “Taking Goma would not be a battle,” said Major Emille Shabani, who had defected from the Congolese army to the rebels a few days before. “The government soldiers are tired and they know no one will look after their families if they die.”

That’s the broad scenario that appeared to have played out Tuesday as M23 rebels rolled into Goma unopposed by government forces, who fled precisely as the rebels predicted, and peacekeepers from Monusco, the Congo U.N. force, who simply watched. Though there had been some sporadic fighting on the outskirts of Goma Monday, loss of life seemed mercifully low. A German newspaper correspondent reported seeing the bodies of a handful of dead government soldiers, but otherwise the streets of Goma were mostly deserted, save for a few M23 soldiers being greeted by small crowds of their supporters. Having raised their hand, the rebels appeared ready to sit back and wait for Kinshasa’s reaction. “We’ve taken the town, it’s under control,” M23 spokesman Colonel Vianney Kazarama told Reuters, before adding: “We’re very tired. We’re going to greet our friends now.”

Others see the start of something far more sinister in these events. The DRC — its government and army — Human Rights Watch and the U.N., particularly its Group of Experts, which monitors militia violence in the country, say neighboring Rwanda and to a lesser extent Uganda want to take over eastern Congo and its mines, rich in metals and minerals such as gold, coltan and diamonds. Their instruments for doing this, they say, are the M23 — largely ethnically Rwandese — and other militias that they supply with funds and weapons to foment chaos across the region. The strategy, they say, is this: Congo’s east is a place where the authority of Kinshasa is nonexistent. The ill-disciplined, underpaid and inadequately supplied Congolese army has little stomach for a fight, while Monusco troops have in the decade of their existence demonstrated a profound disinterest in keeping much of a peace, let alone intervening in any actual fighting. With eastern Congo in chaos, Rwanda will have created a situation in which, whatever anyone else’s misgivings, there would be little alternative to inviting the Rwandans to intervene to end the fighting — given the discipline and capabilities of the Rwandan army — and, by default, take over.

There is some merit to this analysis, foremost in the way it recognizes the weakness of so many of the players. That’s a truth some of those players have yet to digest. On Monday President Kabila vowed his forces would fight. “When war is imposed on us, we have an obligation to resist,” he said. Hours later they fled Goma almost without firing a shot, though not before looting a number of businesses and houses.

What the M23’s advance also does, undeniably, is enhance the authority of Congo’s eastern neighbors, Rwanda and Uganda. Underlining that point, on Monday, U.N. Secretary-General Ban Ki-moon called on Rwandan President Paul Kagame to “use his influence on the M23 to help calm the situation and restrain M23 from continuing their attack”; while on Tuesday, Kabila flew to the Ugandan capital, Kampala, for talks with President Yoweri Museveni. The DRC, U.N. and Human Rights Watch will see the takeover of Goma as the partial fulfillment of a conspiracy hatched in Kigali and Kampala. But there is also little doubt that for the Congolese government and army, and the world’s biggest peacekeeping force, it is confirmation of a basic law of human and military physics: create a vacuum, or at least allow one, and someone will eventually fill it.